BRUSSELS (CNN) -- As NATO monitored the demilitarization of
the Kosovo Liberation Army, the alliance's supreme military
commander warned Sunday that Serb paramilitaries who remain behind will have to turn in their weapons or face KFOR action.

"In a number of locations, it's clear that Serb
paramilitaries, some with connections with intelligence
organizations and others, have remained behind," Gen. Wesley
Clark said on NBC's "Meet the Press."

"Whether this is some effort to report on situations there,
whether it's the seeds for a future conflict to contest
control of the province, no one knows," he said.

"But it is a violation of the MTA for these groups to be
there," Clark said, referring to the military-technical
agreement governing the Yugoslav withdrawal from Kosovo.
"They're going to have to disarm and convert, or they're going to have to leave."

The general said the KLA's demilitarization is set to begin
Monday.

"They'll be putting their weapons into joint custody with
KFOR forces, and I think this is a program that's timely,"
said Clark. "It's been well-handled thus far by KLA
leadership, and we're hoping for full compliance with the
undertaking they've made with NATO."

The problems of maintaining the fragile peace became more
evident Sunday as NATO peacekeepers reported the shooting
deaths of two people in Pristina.

KFOR officials told CNN that the victims were a man and a
woman. The man was a former member of the Organization for
Security and Cooperation in Europe, the monitoring agency
that pulled out of Kosovo prior to NATO's air campaign; the
woman was his interpreter, KFOR spokesman Louis Garneau said.

Both were shot outside an apartment building at close range,
with eight or nine shots fired from what is believed to be
two different caliber guns. There has been no word on who may
have perpetrated the attack.

The president of CARE USA said such acts of violence,
especially among returning refugees and displaced persons,
also pose a threat to those who are trying to provide
humanitarian aid.

"We're very troubled by this news. It just underscores the
fact that security for the refugees, the displaced persons,
humanitarian workers needs to be a first concern," CARE
President Peter Bell told CNN.

In Gnjilane, the U.S. peacekeeping contingent had its first
military injury, when a KFOR patrol of Marines came under
fire while responding to reports of burning homes.

A Marine was slightly injured in the cheek and required a few stitches.

The source of the gunfire remains unclear.

Relief workers and KFOR troops alike have their hands full
after the end of NATO's 11-week bombing campaign against
Yugoslavia. NATO's purpose in targeting Yugoslav troops and
Serb paramilitaries was to stop what it called Yugoslavia's
systematic policy of "ethnically cleansing" the Kosovo region
of ethnic Albanians.

But now that Kosovo's Albanians are returning to their homes,
the province's Serbs have begun to flee, fearing reprisals.

In some cases, those fears have proven true. Italian soldiers
found the body of a Serb woman in Belo Polje, a burning
village being looted by Albanians. The woman's mother said
uniformed Albanians killed her daughter.

In other villages, frightened Serbs have reported widespread
looting. But many of the Albanians say they are only doing to
the Serbs what was done to them.

"The Serbs took everything from us, and I have to have
something to feed my eight children," said Gjyste Gjokaj.

In Kosovo's second largest city, Prizren, German Brig. Gen.
Fritz von Korff said his troops were imposing a curfew to
help control the looting and stealing that have hampered
their efforts to impose order.

Kosovo received its first visit from a NATO head of state
since the alliance launched its bombing campaign against
Yugoslavia on March 24. Czech President Vaclav Havel visited
Prizren and praised German peacekeepers there.

The U.N. refugee agency said it will start its first
organized return of refugees from camps in neighboring
countries. So far, nearly 400,000 of 860,000 ethnic Albanians
have come home on their own, many of them to find ruined
homes and dead relatives.

U.S. Ambassador for War Crimes David Scheffer said, "Our worst assumptions are being borne true in Kosovo," referring
to continuing discoveries by KFOR troops of mass graves and
mass killing sites.